1. Field of the Invention
This invention is concerned with an improved process for converting synthesis gas, i.e., mixtures of gaseous carbon oxides with hydrogen or hydrogen donors, to hydrocarbon mixtures.
2. Description of the Prior Art
Processes for the conversion of coal and other hydrocarbons such as natural gas to a gaseous mixture consisting essentially of hydrogen and carbon monoxide and/or dioxide are well known. Those of major importance depend either on the partial combustion of the fuel with an oxygen-containing gas or on the high temperature reaction of the fuel with steam, or on a combination of these two reactions. An excellent summary of the art of gas manufacture, including synthesis gas, from solid and liquid fuels, is given in Encyclopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume 10, pages 353-433 (1966), Interscience Publishers, New York, New York,.
It is also well known that synthesis gas will undergo conversion to reduction products of carbon monoxide, such as hydrocarbons, at from about 300.degree. F. to about 850.degree. F., under from about one to one thousand atmospheres pressure, over a fairly wide variety of catalysts. The Fischer-Tropsch process, for example, which has been most extensively studied, produces a range of liquid hydrocarbons, a portion of which have been used as low octane gasoline. Catalysts that have been studied for this and related processes include those based on iron, cobalt, nickel, ruthenium, thorium, rhodium and osmium, or their oxides.
The conversion of synthesis gas into valuable products can be greatly enhanced by employing a special type of crystalline aluminosilicate zeolite exemplified by ZSM-5 or ZSM-11 in admixture with a conventional Fischer-Tropsch catalyst. Thus, for example, in copending application Ser. No. 463,711, filed April 24, 1974, there is disclosed a process for the conversion of syngas by passing the same at elevated temperature over a catalyst which comprises an intimate mixture of a Fischer-Tropsch component and a special type of zeolite such as ZSM-5. Said copending application points out that the products produced by hydrocarbon mixtures which are useful in the manufacture of heating oil, high octane gasoline, aromatic compounds and chemical intermediates.
As can well be appreciated, the patent and technical literature relating to the Fischer-Tropsch process, is, indeed, extensive and the various catalysts reported in the prior art have been used by themselves as well as in admixture with catalytically inactive supports such as kieselguhr. Although the reasons for using catalytically inactive supports have varied, nevertheless, it would appear that one reason for using the same was that it resulted in increased surface area of the Fischer-Tropsch component upon which it was deposited or admixed and that it also aided in controlling the heat requirements of the overall exothermic reactions.
It is also known in the art to admix a Fischer-Tropsch component with a material, such as silica alumina which is known to be catalytically active for the conversion of hydrocarbons. U.S. Pat. No. 2,637,739 discloses a Fischer-Tropsch process involving the conversion of syngas by passing the same over a Fischer-Tropsch catalyst in admixture with silica alumina.
U.S. Pat. No. 3,894,102 is directed towards a two-stage process for the conversion of syngas wherein the first stage a methanol synthesis catalyst is admixed with an acidic dehydrogenation catalyst and the product thereof contacted with an HZSM-5 type aluminosilicate zeolite.
In copending application Ser. No. 793,015, filed May 2, 1977, there is disclosed a method for producing an olefinic gasoline by contacting a syngas with a catalyst mixture comprising two components, one being a cobalt containing Fischer-Tropsch component and the other being a ZSM-5 type aluminosilicate zeolite wherein the activity of the ZSM-5 type aluminosilicate zeolite is balanced with the activity of the cobalt containing Fischer-Tropsch component. The product resulting from this type of conversion is an olefinic gasoline wherein the olefins are predominantly branched 8&gt;50 percent) and internal due to the action of the ZSM-5 type component.
In copending application Ser. No. 793,016, filed May 2, 1977, now abandoned there is disclosed a method for producing an olefinic gasoline by contacting a syngas with a catalyst mixture comprising two components, one being an iron-containing Fischer-Tropsch component and the other being a ZSM-5 type aluminosilicate zeolite wherein the activity of the ZSM-5 type aluminosilicate zeolite is balanced with the iron-containing Fischer-Tropsch component. The product resulting from this type of conversion is an olefinic gasoline having a clear research octane number greater than 85 wherein the olefins are predominantly branched (&gt;50 percent) and internal due to the action of the ZSM-5 type of component.
Also copending is application Ser. No. 775,129, filed Mar. 7, 1977 which is concerned with the conversion of syngas over a catalyst comprising a Fischer-Tropsch component and an acidic cracking catalyst and is also directed towards balancing the activity of the acidic component with the Fischer-Tropsch catalyst. However, the product obtained from the process of said copending application is an olefinic product wherein the olefins have predominantly internal (&gt;50 percent) double bonds and the gasoline has a clear research octane number greater than 75. The solid acidic component utilized in the process of this copending application is not a ZSM-5 type zeolite, but rather it includes the use of an amorphous material, such as silica alumina, as well as the more conventional type crystalline aluminosilicates, such as faujasite, erionite, mordenite, etc., that are capable of sorbing n-hexane.
U.S. Pat. No. 3,013,990 suggests a catalyst composition useful in process including Fischer-Tropsch synthesis (see Column 10, lines 71-74) which composition comprises a zeolite molecular sieve containing a substantial quantity of at least one material selected from the group consisting of Fe, Co, Ni, and oxides thereof in the internal adsorption area of the zeolite molecular sieve. At Column 1, lines 38-39, "zeolitic molecular sieves" are defined as "metal aluminosilicates", and all the zeolites disclosed have a relatively high ratio of alumina:silica. None of the zeolites have the composition or characteristic x-ray powder diffraction pattern of the silica zeolite component recited in the present claims. However, the patent does not discuss the preparation of gasoline-boiling-range hydrocarbons.
The ZSM-5 type crystalline zeolite component of the intimate catalyst mixture recited in the present claims is disclosed in U.S. Pat. No. 3,941,871. The uses suggested therein for the crystalline zeolite catalyst are hydrocracking, catalytic cracking, reforming, hydroisomerization of normal paraffins, and olefin isomerization (Column 5, line 54 to Column 6, line 22). No process is discussed for the direct conversion of synthesis gas to gasoline-boiling-range products.